1. Field of the Invention
This invention relates to a system for monitoring the efficacy of a process of sterilization in a manner that prevents the contaminating effect of airborne microorganisms and that permits incubation of test spores without culture media loss.
2. Description of the Prior Art
In the field of sterilization of articles, it is desirable to ascertain whether a particular load of articles that is subjected to a sterilizing environment, either steam or gas, has in fact been exposed to an environment which would have killed microorganisms at an acceptable rate. This objective may be carried out in a variety of ways but generally involves subjecting a known number of test spores to the same sterilizing environment, under the same conditions, as that to which the articles in the sterilizer are subjected. Upon completion of the sterilization cycle, the test spores are removed from the sterilizer and are exposed to a growth-inducing medium. The test spores so exposed are incubated for a specified time period and then are checked for spore growth. If no microbiological growth occurs, it can be assumed that the articles in the particular load tested are "sterile" for their intended purpose. If, on the other hand, growth is observed, the articles may not be deemed "sterile" and should be subjected to a completely new sterilization cycle.
In order to guarantee the accuracy of the test just described, it is, of course, necessary that the test spores be exposed to the sterilizing environment within the sterilizer; this means that the container used for the test spores must be open to the surrounding atmosphere. But after the sterilization cycle is complete and the sterilizer is opened, the test container must be removed from the sterilizer and thereby is subjected to a nonsterile environment while the manipulations required to bring the spores into contact with the growth medium are carried out. During this period, airborne microorganisms present in the environment may be introduced into the test container and render the subsequent sterilization tests unreliable.
Workers in the art have recognized this problem and their efforts to remedy it generally have centered around providing some sort of shielding means around the test container, such as a membrane or filter that generally is penetrable by sterilant but is impenetrable by airborne microorganisms; see, e.g., U.S. Pat. Nos. 3,661,717 and 3,440,144. The existence of any barrier to the free flow of sterilizing environment to the test spores during sterilization, however, may cast doubt upon the validity of the sterilization test.
Further, the known biological indicating systems suffer an additional disadvantage relating to the required incubation period. Because the known systems are constructed at least in part of materials that are permeable to the sterilizing environment, they are subject to media loss through evaporation when the test container is subjected to incubation temperatures. This problem is solved in the known systems by the use of special incubation equipment in which the humidity and thus media evaporation rates are reduced. However, the introduction of water vapor into an enclosure containing the test system offers an opportunity for extraneous contamination of the test components because the test container is not sealed during the incubation period.